Papers by Keyword: Metallic Glass

Abstract: Fine nanoporous copper was fabricated from the amorphous Ti-Cu alloys with a minor addition of silver in 10 mM HF solutions. The pore sizes decreased from 100 nm to 12 nm with the increase of the Ag contents in comparison of Ti₆₀Cu₄₀ ribbons free of Ag. With increasing of the dealloying time, the sizes of the nanopores and ligaments increased for the nanostrucutres on Ti₆₀Cu₃₈Ag₂ ribbons since the segregation of the Ag phase which triggered the galvanic dissolution of the adjacent Cu matrix in form of micro-couplings to further coarsen the nanoporous Cu. On the contrary, the trace formation of the Ag phase on the Ti₆₀Cu₃₉Ag₁ ribbons had a weak ability to motivate the galvanic dissolution, indicating by the constant pore sizes and slight decrease in the ligament sizes with the increase in the dealloying time. The refinement of the nanoporous structures was ascribed to the drastic decrease in the surface diffusivity. The decrease in the surface diffusivity due to the involvement of Ag with a lower surface diffusivity in comparison of Cu was more than one order of magnitude. The involvement of Ag adatoms restricted the diffusion of Cu adatoms in the interface regions in the inward and outward directions.

Abstract: Monolithic uniform nanoporous Cu (NPC) ribbons with a ligament/pore size of 10-25 nm are successfully synthesized by chemical dealloying the Cu₅₀Zr₅₀ and Cu₅₀Zr₄₅Al₅ metallic glasses in 0.5 M HF for 7 min. It is found that the length scale of ligaments/channels can be tuned by simply alloying 5 at.% Al to the Cu-Zr binary glassy alloys. The current signal of the NPC-supported MnO₂ composite electrode is remarkably enhanced as compared to that of pure MnO₂ powders. These new findings greatly raise the hope for possible applications of NPC as a new type of electrode substrates or an advanced sensor in green and new energy technology.

Abstract: The amorphous alloy films of ZrCu and AgMgAl, layers deposited by co-sputtering was utilized as the metallic layer in the bi-layer structure transparent conductive electrode of ZrCu/ITO and AgMgAl/ITO deposited on the PET substrate using magnetron sputtering at room temperature. In the transmittance performance, the 30 nm ITO/3 nm ZrCu and 30 nm ITO/15 nm AgMgAl films could show the optical transmittance of 73 % and 70% at visible light of 550 nm wavelength and maintain the stable transmittance of 70~75% from visible light to infrared region. Meanwhile, the 30 nm ITO/9 nm ZrCu and the 30 nm ITO/15 nm AgMgAl films could show the better sheet resistance of 136 Ω/sq. and 135 Ω/sq. respectively. In addition, compared with the ITO film, the current metallic glasses were utilized as the metallic layer in the bi-layer structure transparent conductive electrode showed the better bending properties. The relative change of resistivity is below 0.4, significantly lower than that of the commercial PET/ITO product. The ZCI would exhibit lower variation in resistance owing to short crack propagated in the amorphous alloy of ZrCu layer after 10000 cycles bending test.

Abstract: MgZnCa amorphous matrix-based composites whereby reinforcing the matrix with suitable reinforcements to achieve enhanced mechanical, biomedical and anti-corrosion properties have been studied here. Here, MgZnCa-based composites have been developed with different amounts (0-25%wt) of yttria-stabilized zirconia (YSZ) reinforcement phase. The aim is to understand the corrosion behaviors of YSZ-reinforced MgZnCa-based composites in physiological saline solution. It is found that the incorporation of YSZ into amorphous MgZnCa matrix can cause crystallization of the amorphous matrix. The higher the YSZ introduced, the higher the degree of crystallization, and a fully crystalline matrix is obtained at a YSZ concentration of 25%. Electrochemical testing and ion release measurements, revealed that the composite with 8%YSZ possesses the smallest corrosion current density and the least ion release rate. Surface morphology analysis indicates a much stronger anti-corrosion ability of 8%YSZ-reinforced MgZnCa composite.

Abstract: New Ti-based ternary metallic glasses were designed and fabricated. A new parameter called effective atomic radius in the Ti solid solution from ab-initio calculation was used to design of the Ti-based metallic glasses. From the effective atomic radius, Ti-Zr-Mn, Ti-Zr-Fe and Ti-Zr-Co systems can be considered as a new Ti-based ternary metallic glass. And the reported scheme based on the concept of binary eutectic clusters is applied to predict alloy composition which shows glass transition.We prepared the Ti₄₂Zr₂₂Mn₃₆, Ti₄₃Zr₂₉Fe₂₈ and Ti₄₄Zr₃₀Co₂₆ alloy sheets by a single-roller method. It showed that sharp diffraction peak corresponding to crystalline phases could be observed in the XRD spectra of Ti₄₂Zr₂₂Mn₃₆ and Ti₄₃Zr₂₉Fe₂₈. While for alloy with Ti₄₄Zr₃₀Co₂₆ no sharp diffraction peak could be found except broad diffraction halos. This result suggests that a critical eutectic temperature in the phase equilibrium for forming glass phase is around 1000°C.

Abstract: The subject of this study is the change of the electrical resistivity of Fe-based metallic glasses during heat treatment. Electrical resistivity is a structure-sensitive characteristic of materials. In metallic glasses, the scattering of conduction electrons on the disordered structure is the main mechanism responsible for the electrical resistivity. Hence amorphous metallic alloys have a much higher residual resistivity as compared to their crystalline analogs. It is typical for metallic glasses that the temperature coefficient of resistivity (TRC) is smaller than for the corresponding crystalline materials, and it can be either positive or negative.

Abstract: In this paper the analysis of structure changes in series of amorphous alloys with different Fe/Ni and Fe/Co ratio and Cr addition is made. It has been shown that within temperature range 23⁰С <T< 450⁰С the structure of alloys keeps its amorphous character and only a slight changes in heat flow occur. At temperatures above 450°C the structure evolution depends of the Fe/Ni and Fe/Co ratio and some dopants.

Abstract: Firstly, this paper reminds the reader of some basic facts about the glassy state, then of the various ways to produce amorphous metals with particular emphasis on the route of vitrification from the melt. Vitrification of an undercooled melt is the most important route from the viewpoint of the application of metallic glasses. We compare diffusion in some metallic glasses with related crystalline metals. Glassy metals, also called metallic glasses, comprise conventional [1] and bulk metallic glasses [2,3]. We remind the reader of the major experimental techniques for diffusion studies in metallic glasses. The paper then reviews our current understanding of diffusion in glassy metals (see also [4,5,6]), including conventional as well as bulk metallic glasses and undercooled melts. We cover the temperature dependence of diffusion in metallic glasses and discuss the spectrum of activation parameters of glassy metals and its difference to the corresponding one of crystalline metals. We mention the pressure dependence and the isotope effect and we discuss tracer diffusion and viscosity diffusion for a bulk metallic glass and its undercooled melt. Finally we mention computer simulations of atomic jump processes. The diffusion mechanism in metallic glasses differs from that in crystalline metals and involves thermally activated, highly collective (chain-like or caterpillar-like) diffusion jumps. Finally, we mention diffusion along shearbands in a plastically deformed glassy metal.

Abstract: The uniaxial tensile tests are generally used to measure the yield stress and/or tensile stresses. The majority of the results, resulting from this method and deferred in the literature on the mechanical properties of amorphous materials, were obtained in the ribbons form generally produced by melt spinning. This limitation in the shape of the specimens for tensile tests was inherent in the manufacturing techniques of the amorphous materials which required cooling rates of about 10⁶ °C/s. The fabrication of amorphous coatings by plasma spraying, in tubular form, should improve rigidity of the specimens, increase their size and especially get a more reliable means to the amorphous coatings under the tensile test. Amorphous coatings of NiCrBSi alloys are produced by thermal plasma spraying. The thickness of the resulting amorphous deposit may be up to 500 μm. The uniaxial tensile tests were carried on Instron machine at room temperature. Microstructural studies are investigated by means of X-ray diffraction (XRD), scanning (SEM) and transmission (TEM) electron microscopy. The test methodology used in this study shows that it is possible to obtain a comprehensive assessment of the mechanical properties of the amorphous coatings deposited by thermal plasma in tubular form. Plasma sprayed coatings in tubular form, under the uniaxial tensile test in the amorphous state, crystallized and nanocrystallized, fracture without bursting compared to samples in the form of amorphous ribbon.

Abstract: This study reports the glass forming ability (GFA) of Al-Ni-Si alloys with selected compositions based on atomic packing efficiency and driving force criteria. Higher GFA was observed in the Al-rich lower liquidus temperature regions of the Al-Ni-Si system indicating that these compositions exhibit a lower driving force for crystallization. Five glassy alloys that were calculated to consist of densely packed atomic short-range ordering were found to retain an amorphous structure upon copper mould casting. The result of GFA in the Al-Ni-Si system provides a novel approach to develop new metallic glasses considering both the thermodynamic stability and sluggish crystallisation kinetics through efficient packing.